doxygen: URL and version hashes updated to project's GitHub home (#10250)
doxygen: URL and version hashes updated to project's GitHub home (#10250)

* Update package.py

Doxygen has migrated from a private SVN to GitHub. This PR updates the URLs and adds versioned commit hashes from GitHub. It also includes version 1.8.15 as the latest option.

* Update package.py

LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack